The invention relates to a method of manufacturing a semiconductor device whereby a reaction chamber in which a layer of material is deposited on a semiconductor slice placed on a support in the reaction chamber, whereby a process gas is conducted towards the slice through a gas inlet system which is provided with a perforated gas inlet plate arranged opposite the support, between depositions is cleaned periodically through the generation of a plasma between the support and the gas inlet plate in a gas mixture comprising fluorine or a fluorine compound and oxygen or an oxygen compound.
During such a deposition process, for example, a layer of silicon, silicon oxide, silicon nitride, tungsten, or titanium nitride is deposited on the semiconductor slice. During this, the slice is heated to a temperature of 400.degree. to 800.degree. C. in a chemical vapour deposition process, after which the process gas is conducted towards the slice. In the case of a plasma-enhanced chemical vapour deposition process, a plasma is generated between the support and the gas inlet plate. The said process gas then comprises a gaseous silicon compound, a gas mixture comprising a silicon compound and oxygen or an oxygen compound, a gas mixture comprising a silicon compound and nitrogen or a nitrogen compound, a tungsten compound, and a titanium compound, respectively. Usual silicon compounds are silane, dichlorosilane and tetraethoxysilane, while a usual oxygen compound is laughing gas and a usual nitrogen compound ammonia.
The process gas is conducted towards the slice placed on the support through a perforated gas inlet plate which is positioned opposite the support. The gas inlet plate is, for example, an aluminium plate in which a large number of holes with a diameter of, for example, 1 mm are provided, regularly distributed over its surface. The plate may also be manufactured from a porous material, such as sintered aluminium powder. Such a plate is perforated by means of channels which are present in the sintered material. The use of such a perforated gas inlet plate achieves that the process gas is homogeneously distributed over the slice, so that a homogeneous deposition is obtained. The gas inlet plate has a diameter which is at least equal to that of the slice.
A support for a single slice may be arranged in the process chamber, but alternatively there may be a support on which several slices may be arranged next to one another. In the former case, the chamber comprises a gas inlet system with a single gas inlet plate, in the latter case one with a comparatively large gas inlet plate or with several gas inlet plates.
During the deposition process a layer of material is deposited not only on the slice, but also on chamber components which are situated near the slice. When the deposition process is repeated, layers being deposited on subsequent slices, the layer on these chamber components increases in thickness. When the layer on the chamber components becomes too thick, particles may flake off from this layer and end up on the slice. These particles are undesirable there. Accordingly, the reaction chamber must be cleaned periodically.
An effective cleaning can be obtained when the reaction chamber is cleaned through generation of a plasma between the support and the gas inlet plate in a gas mixture comprising fluorine or a fluorine compound and oxygen or an oxygen compound which is conducted into the reaction chamber. Practical gas mixtures are, for example, a mixture of CF.sub.4 and O.sub.2, a mixture of SF.sub.6 and N.sub.2 O, or a mixture of C.sub.2 F.sub.6 and O.sub.2, which exhibit a maximum cleaning effect when 10 to 30 vol. %, 30 to 50 vol. % and 40 to 60 vol. % O.sub.2 are added to them, respectively. The materials mentioned above can be very effectively removed by means of such plasmas.
U.S. Pat. No. 4,960,488 discloses a method of the kind mentioned in the opening paragraph whereby the gas mixture is conducted into the reaction chamber through the gas inlet plate.
It is found with the use of the known method that the chamber components close to the slice can be well cleaned. The known method, however, also has disadvantages. Thus the gas inlet plate is sometimes locally attacked by the cleaning process and sometimes undesirable particles still end up on the slices. Practically no particles arrive at the slices any more which contain the material which is deposited in the reaction chamber during the deposition process, but particles of a material having a different composition do. It is found that the composition depends on the fluorine compound used during cleaning. When a fluorine-carbon compound is used, the particles contain carbon, when a fluorine-sulphur compound is used, the particles contain sulphur.